What does it mean?
OBD II fault code P0470 is a generic code that is defined as “Exhaust Pressure Sensor “A” Circuit” , and is set when the PCM (Powertrain Control Module) detects a failure, malfunction, or defect in the reference and/or signal circuit(s) of the exhaust back pressure sensor that is labelled “A”.
Note that since some applications may have more than one exhaust backpressure sensors, it is recommended that the manual for the affected application be consulted to locate and identify exhaust backpressure sensor “A” correctly. Although exhaust backpressure sensors are used on many gasoline-powered applications, this sensor is most commonly found on turbo diesel applications, on which this sensor plays a critical role in emission control.
In practice, an exhaust backpressure sensor is used to measure the amount of backpressure in an exhaust system. In most cases, and especially on diesel applications, the amount of exhaust backpressure is directly related to the amount of particulate matter (soot) that is being held captive by the DPF (Diesel Particulate Filter).
Since an excessive amount of soot in the DPF effectively clogs the exhaust system, thus impeding the free flow of exhaust gas through the system, the PCM interprets the actual exhaust back pressure as a measure of how clogged the DPF is.
When the PCM deems the DPF to be clogged (based on input data from the exhaust backpressure sensor), it will initiate a process known as DPF regeneration either by injecting a reactant into the exhaust, or by raising the exhaust gas temperature by injecting raw fuel into the exhaust to burn off the accumulated soot. In terms of operation, the exhaust backpressure sensor is supplied with a 5-volt reference voltage by the PCM.
As the pressure in the exhaust changes, the electrical resistance of the sensing element changes as well, with the result that more or less voltage is passed back to the PCM via a dedicated signal circuit, with the changing signal voltage being interpreted by the PCM as changes in pressure.
It should be noted, that on some applications, the input data from the exhaust back pressure sensor is also used by the PCM to monitor/control turbo charger boost pressure, in addition to monitoring / regulating the operation of the EGR (Exhaust Gas Recirculation) system.
However, and regardless of the systems the exhaust gas backpressure sensor is associated with on any given application, the PCM depends on reliable, accurate, and plausible input data from the sensor if all associated systems are to work as expected.
Thus, if the PCM detects any malfunction, defect, failure, or fault in the exhaust back pressure sensors’ control / signal system that prevents the exhaust back pressure system from generating, or delivering accurate input data, it recognizes that it cannot monitor the exhaust pressure effectively, and it will set code P0470, and may also illuminate a warning light as a result.